Procedure and device for protecting vehicle occupants

ABSTRACT

A device for the protection of occupants of a vehicle includes at least one acceleration sensor (10), an electronic device (20) for evaluating the output signal of the sensor (10), and a protective device (30) for the occupants of the vehicle. The electronic device makes it possible to carry out a process for the activating in due time of the protective device (30) by the electronic device (20) in the manner that estimated values for the future displacement of the occupant of the vehicle and/or his relative speed with respect to the passenger compartment are estimated in advance and compared with presettable limit values.

BACKGROUND INFORMATION

Traffic accidents which endanger the occupants of a vehicle, such as,for instance, impact of the vehicle against a stationary obstacle orcollision with another vehicle, is an occurrence which proceedsextremely rapidly and lasts for only about 100 milliseconds from thefirst contact with the obstacle until its end. On the other hand,protective means for protecting the occupants from injury in anaccident, such as safety belts and/or airbags, require a certain minimumamount of time for their activation. By activation, there is understood,for instance, in the case of an airbag, the procedure which extends fromthe igniting of the gas injection charge until the airbag has beeninflated into its protective position. For this, a few dozenmilliseconds are required. In the protective systems described abovethere is therefore the problem, in particular, of noting the potentialfor endangerment in an accident as early as possible in order to be ableto activate the protective system provided in the vehicle so rapidlythat, taking into account the time for its activation, it can stillcontribute to protecting the occupant. For example, an airbag must beinflated sufficiently early that the occupant who is greatly acceleratedby the forces occurring upon the accident does not strike his head onparts of the vehicle, for instance the steering wheel, and therebyseriously injure himself. On the other hand, the triggering mechanismfor the protective system must not be so sensitive that it responds andactivates the protective system at values of acceleration which are notdangerous for the occupants. This would namely result in a high expensefor the repair of the unnecessarily activated protective system.

There have been numerous attempts to solve this difficult problem. Thus,a protective device is known from U.S. Pat. No. 4,020,453 which has anacceleration sensor which notes the acceleration of the vehicle and inwhich the acceleration signal is integrated and the protective systemtriggered when the integrated acceleration value has exceeded athreshold value which can be preset. In this known safety devicetherefore, an integrated acceleration value can be preset by a thresholdvalue which is considered so dangerous that the activating of theprotective system is then necessary. This known safety device disregardsthe position in which the occupant to be protected is actually sitting,and which may differ greatly from case to case. For example, theoccupant may be sitting with his back pressed firmly against thebackrest of the car seat or he may have his head in the vicinity of theinstrument panel in order, for instance, better to read a display.However, the optimal protective action of the protective system dependson the position in which the passenger in the vehicle is actuallysitting.

Therefore, attempts have also been made to note the actual position ofthe passenger and take it into account for activation of the protectivesystem. Such protective systems are known, for instance, from GermanyPatent Application Nos. DE 40 05 598 A1, DE 38 09 074 A1 and DE 40 23109 A1. These last-mentioned solutions are, however, comparativelyexpensive since they require additional sensors such as, for instance,seat contacts, ultrasonic barriers, light barriers or the like, in orderto note the actual position of the passenger. The application of suchadditional sensors and evaluation means for them to different vehicles,and possibly also their adaptation to the different shape of occupantsof the vehicle, means a large expense for construction and maintenance.Finally, these additional components may also, as a whole, impair thereliability of the protective system, since defects can occur in thewires and contact means necessary for the connecting of the sensors andevaluation units.

In accordance with a further solution of the problem described above, ithas, it is true, been attempted, in accordance with Germany PatentApplication No. DE 38 03 426 A1, to take the actual position in whichthe occupant of the car is sitting into consideration in connection withthe activating of the protective system. In accordance with this knownsolution, however, the actual position in which the occupant is sittingis no longer noted by sensors, but it is attempted to calculate theforward displacement of the occupant which occurs as a result ofacceleration by means of the acceleration of the vehicle noted by anacceleration sensor on the basis of a mathematical formula. For the useof this formula, the occupant is considered to be a freely movable masswith respect to the vehicle. Further influences, such as, for instance,the supporting of the driver on the steering wheel, the spring action ofthe vehicle seats and the like, can be taken into account in the mannerthat corresponding correction factors describe the forward displacementof the occupant in the manner of a massspring system.

Proceeding from this known prior art, the object of the presentinvention is to improve the triggering of a protective system for theoccupants of vehicles by also taking into account the actual position inwhich the occupant is sitting.

SUMMARY OF THE INVENTION

The present invention, in particular, offers the advantage that theactivation in due time of the protective means provided for theoccupants of the vehicle is made possible with due consideration of thedisplacement of the occupant as the result of acceleration or therelative speed of the passenger with respect to the passengercompartment resulting from the acceleration even without additionalsensors which detect the position of the passenger. The activating indue time of the protective means is obtained, in particular, by anestimate of the forward displacement of the occupant which is to beexpected within the activation time. This estimate permits aparticularly rapid response of the protective means and makes certainthat the protective means are activated in due time in the event ofdanger in order to perform their protective function. This estimate iseffected in a particularly suitable manner by means of a smoothedacceleration curve which is obtained by filtering from the actualacceleration measurement signal. Kalman filtering is used to particularadvantage. The course of the smoothed acceleration curve can beapproximated by a known function, which can be readily controlled, sothat acceleration values lying ahead in the future can be determinedwith relatively little expense.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a protective system according to thepresent invention for protecting vehicle occupants.

FIG. 2a shows an acceleration signal output as a function of time from asensor according to the present invention.

FIG. 2b shows the relative speed of an occupant of a vehicle withrespect to the passenger compartment of the vehicle as a function oftime.

FIG. 2c shows a forward displacement curve of an occupant of a vehiclewith respect to time.

FIG. 3a shows an acceleration signal output as a function of time from asensor according to the present invention when a vehicle is subjected toan acceleration in the direction of its lengthwise axis.

FIG. 3b shows the relative speed of an occupant of a vehicle withrespect to the passenger compartment of the vehicle as a function oftime when the vehicle is subjected to an acceleration in the directionof its lengthwise axis.

FIG. 3c shows a forward displacement curve of an occupant of a vehiclewith respect to time when a vehicle is subjected to an acceleration inthe direction of its lengthwise axis.

FIG. 4a shows an acceleration signal output as a function of time from asensor according to the present invention in the case of an idealizedstandard body at speeds of 20 km/hr, 40 km/hr and 60 km/hr.

FIG. 4b shows an acceleration signal output as a function of time from asensor according to the present invention in the case of an idealizedsoft body at speeds of 20 km/hr, 40 km/hr and 60 km/hr.

FIG. 4c shows an acceleration signal output as a function of time from asensor according to the present invention in the case of an idealizedhard body at speeds of 20 km/hr, 40 km/hr and 60 km/hr.

FIG. 5 shows acceleration curves with respect to time of a hard body,standard body and soft body.

FIG. 6 shows acceleration curves with respect to time of a hard body,standard body and soft body where the crash time is independent of thetype of body.

FIG. 7 shows another set of acceleration curves with respect to time ofa hard body, standard body and soft body where the crash time isindependent of the type of body.

FIG. 8 illustrates the acceleration-dependent displacement of anoccupant of a vehicle in the event of a negatively directed action ofacceleration.

FIG. 9 shows a limit speed value of an occupant of a vehicle withrespect to the passenger component of the vehicle as a function ofaverage acceleration.

FIG. 10 shows a limit curve according to the present invention havingpresettable limit values plotted with respect to time.

FIG. 11 shows an acceleration signal output as a function of time from asensor according to the present invention upon an accident.

FIG. 12 shows a signal output from a sensor according to the presentinvention upon an accident, together with a limit curve.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a block diagram of a protective system for the occupants ofvehicles. This protective system comprises at least one sensor 10 whichnotes accelerations of the vehicle and is of known type, and mayconsist, for instance, of a piezoelectric ceramic or of strain gaugeswhich are acted upon in each case by a seismic mass. Upon the action ofa force on the seismic mass as a result of an acceleration, the sensor10, for example, gives off an output voltage which is proportional tothe acceleration and which is designated a(t) in the block diagram. Thesensor 10 is connected to an electronic device 20 which processes theoutput signal a(t) from the sensor 10 which is fed to its input side andon its output side actuates the protective means 30 provided for theoccupants of the vehicle. The electronic device 20 comprises filtermeans 21 for filtering the output signal of the sensor 10. As a resultof the filtration, the output signal a(t) of the sensor 10 is convertedinto the signal a' (t). This signal a' (t) is fed to a comparison device22 which is provided in the electronic device 20 and is preferably partof a microcomputer 23. The electronic device 20 furthermore comprises adevice 24 for establishing a limit value s_(g) for the displacement,particularly the forward displacement, of the occupant, as well as afurther device 25 for setting a limit speed value v_(g) with respect tothe relative speed of the occupant with respect to the passengercompartment. The two devices 24 and 25 are connected to a further device26 which can calculate the displacement and the speed of the occupantsfor a subsequent point in time. The device 26 is connected to anotherdevice 27, the output connection of which is, in its turn, connected tothe microcomputer 23. The device 27 determines whether and possiblywhich of the two values, forward displacement s and speed v, hasexceeded the presettable limit values s_(g) and v_(g). The correspondingvalue is fed to the microcomputer 23. The microcomputer 23 is connectedon its output side to protective means 30 for the occupants of thevehicle. These protective means preferably comprise a first airbag 31for the driver of the vehicle, a second airbag 32 for the front seatpassenger, and possibly safety belts 33 and 34 for at least the driverand the front seat passenger.

In order to facilitate an understanding of the invention, various signalforms as a function of time will first of all be explained below withreference to FIG. 2 and FIG. 3. Thus, FIG. 2a shows the accelerationsignal a(t) of the sensor 10, referred to also as acceleration signal.It has been found in practice that even in the event that the vehicle isadvancing at uniform speed and therefore not subject substantially toany acceleration in the direction of advance or in the oppositedirection, an output signal a(t) of the sensor 10 can be measured whichhas bipolar components which are substantially symmetrical to the zeroline and therefore to the t-axis. One can speak here also of amodulation of the acceleration signal. This modulation is produced byaccelerations of the vehicle body caused as a result of the drivingmovements of the vehicle, these accelerations being measured asacceleration by the sensor 10. FIG. 2b shows the relative speed v(t) ofthe occupant with respect to the passenger compartment as a function ofthe time t. This signal can be obtained by integration from the outputsignal a(t) of the sensor 10. FIG. 2b also shows a course of the signalwhich has substantially bipolar components of comparatively smallamplitude which do not essentially lead to a forward displacement of theoccupant. This forward displacement is shown as curve s(t) in the graphof FIG. 2c, which can be determined by integration from the relativespeed.

FIG. 3 shows the corresponding courses of the signal when the vehicle issubjected to an acceleration in the direction of its lengthwise axis,which occurs, for instance, upon an accident. Thus, FIG. 3a again showsthe output signal a(t) of the sensor 10 as a function of the time t. Amodulated signal form can be noted, which now, however, is only unipolarin essential partial regions, and therefore no longer has componentswhich extend beyond the zero line. FIG. 3b shows the speed signal v(t),which rises substantially linearly except for a modulation due to minoramplitude variations. Finally, FIG. 3c shows the curve s(t) representingthe forward displacement of the occupant, which curve is a quadraticfunction of the time t. After smoothing or filtering, there can beobtained from the modulated output signal a(t) of the sensor 10 shown inFIG. 3a, a curve which in the manner of presentation selected inaccordance with FIG. 3a extends substantially above the zero line andcan be referred to as "core signal".

For an understanding of the invention, the course of this so-called coresignal in the case of different types of vehicle bodies is furthermoreimportant. These types of bodies are explained briefly below withreference to FIG. 4. FIG. 4a shows the course of the output signal a(t)of the sensor 10 as a function of the time t in the case of an idealizedstandard body with different speeds of 20 km/hr, 40 km/hr and 60 km/hras parameters. FIG. 4a shows that, with increasing speed, the amplitudeof the maximum of the signal a(t) also increases, but that the durationof the effect of the acceleration which commences at the coordinateorigin is substantially the same regardless of the speed. Differing fromthis, the signal forms in FIG. 4b and FIG. 4c, which represent aso-called soft body and a so-called hard body, show completely differentcourses of the signal. Thus, FIG. 4b, to be sure, shows amplitude valuesfor the maxima of the course of the curve a(t), and therefore theacceleration signal which increase with increasing speed. However, thesemaxima no longer occur at the same time, and the duration of the effectof the acceleration is of different length. The greatest amplitude withthe shortest duration of the acceleration process is present at thehighest speed of 60 km/hr.

With the so-called hard body which is represented by the forms of thesignal in FIG. 4c, larger amplitudes of the acceleration signal a(t)which are also proportional to the speed can be noted, occurring atdifferent times in the same way as in the case of the soft body inaccordance with FIG. 4b. In contradistinction to the showing in FIG. 4b,however, the duration increases with increasing speed.

The nature of the type of body in question can, with a knowledge of itsconstruction, be determined approximately by means of complex arithmeticprograms; in practice, however, the type of body is ordinarilydetermined empirically in the manner that crash tests are carried outwith an experimental specimen of the vehicle at low speeds such as, forinstance 20 km/hr. As a result of such empirical crash tests with a hardbody, a soft body, and a standard body, the acceleration curves a(t)shown in FIG. 5 are obtained. They, in their turn, show that withdifferent types of bodies, amplitude values of different amount occurupon the action of acceleration, and that furthermore the crash timediffers. Thus, for instance, in the case of the hard body, in which thegreatest amplitude of acceleration occurs, the crash time is at an endalready at the time t_(cr1), while in the case of the soft body, whichis characterized by a comparatively low maximal amplitude in the courseof the acceleration curve a(t), the crash time is at an end only afterthe comparatively long time t_(cr3).

From these results, the surprising relationship can be derived that, asshown in FIGS. 6 and 7, regardless of the nature of the body, there is agiven speed v₀ at which the crash time t_(cr) is independent of the typeof body. The crash time is dependent only on the length of the crusherzone s_(k0) of the vehicle.

The diagram in FIG. 8 explains the acceleration-dependent displacementof the occupant, in particular his forward displacement in the event ofa negatively directed action of acceleration as is particularly presentin the case of an accident. S_(abst) is the maximum path which, forinstance, the head of the occupant of the vehicle sitting in normalposition can move over until striking against the steering wheel or theactivated protective means.

It results from this that with a comparatively slight relative speed ofthe occupant of the vehicle with respect to the passenger compartment, alonger period of time is available for measuring the distance S_(abst)than in the event of a comparatively higher relative speed.

These relationships are of importance with respect to the final time ofactivation of the safety means which, as a rule, is independent of thetype of accident and the type of body. The safety means should namely beactivated so early that it can develop its protective action before theoccupant of the vehicle has moved over the maximum availablenon-critical forward displacement distance S_(abst) Furthermore, FIG. 9also shows the limit speed value v_(g) as a function of the averageacceleration a'. From this graph, it can be noted that the limit speedvalue v_(g), which is a function of the maximum forward displacementdistance S_(abst) indicated in FIG. 8 and of the activating time of theprotective means, must be reduced with increasing acceleration a' inorder still to permit a dependable activating of the protective means.

The findings described above have led to the result that, for any typeof body, optimal protection of the occupants of the vehicle can beassured by activation in due time of the existing safety means if thefuture forward displacement of the occupant of the vehicle caused by theeffect of the acceleration and/or the occupant's future relative speedwith respect to the passenger compartment are estimated, and ifactivating of the safety means takes place when the estimate shows thatthe estimated values exceed presettable limit values within apresettable future time interval. As a presettable future time intervalthere is indicated in this connection the activation time of thespecific protective means, which time is known in each case. In theevent of an airbag which is provided as protective means, thispresettable time interval is therefore between 10 and 50 milliseconds,and preferably between 20 and 40 milliseconds. If the forwarddisplacement of the occupant to be expected during this time interval orhis relative speed with respect to the passenger compartment areestimated in advance, it can be judged whether activation of the safetymeans is necessary at all and whether the time available is sufficientat all for the unfolding of the protective means.

In connection with the presetting of the limit values for thedisplacement of the occupant of the vehicle and/or his relative speedwith respect to the passenger compartment, the geometry and/or thestructure of the passenger compartment and/or of the protective meansare advisedly taken into account since they can be dependent on thespecific construction. The permissible forward displacement distanceS_(abst) is preferably established between about 5 and 30 cm, andpreferably between 10 and 20 cm, while the relative speed of theoccupant of the vehicle is fixed at between 5 to 30 km/hr, andpreferably between 10 and 20 km/hr.

In a first embodiment of the present invention, fixed values which may,for instance, be dependent on the construction are used, as explainedabove, as presettable limit values.

In one particularly advantageous embodiment of the present inventionhowever, there are used as presettable limit values variable valueswhich are preferably dependent on at least one operating parameter ofthe vehicle. A particularly favorable, early possibility of activationfor the safety means is obtained if the presettable limit values arevariable in time and are selected as a function of the crash time. Insuch a case, at the start of a crash, relatively large limit values arestill provided, but then, with increasing duration of the crash, theyare decreased, i.e. made smaller. The reduction is effected in thisconnection advisedly by a function with respect to time which isrecognized to be particularly favorable.

For estimating the displacement of the occupant of the vehicle which isto be expected within the period of the time taken into account or theoccupant's relative speed to be expected with reference to the passengercompartment of the vehicle, the acceleration signal of the at least oneacceleration sensor 10 is evaluated, in which connection, to be sure,recourse is had to an acceleration curve which has been freed of thehigher frequency modulation peaks, i.e. filtered, and which is derivedadvisedly by means of a filtering process from the output signal a(t) ofthe sensor 10. For this purpose, as already described with reference toFIG. 1, the last-mentioned output signal is fed to a filtering device 21which produces the output signal a(t). In this connection, Kalmanfiltering of the output signal a(t) of the sensor 10 has provenparticularly favorable since particularly reliable estimates could bemade possible by means of this filtration. In a first embodiment of thepresent invention in which only a comparatively slight expense inconnection with the processing of the output signal of the sensor 10 isnecessary, either only an advance estimate with respect to the forwarddisplacement of the occupant of the vehicle or, as alternative, withrespect to the relative speed to be expected is effected. If necessary,the calculations can be repeated several times in order to improve theprecision.

In another, more expensive embodiment of the present invention,estimated values for the expected forward displacement of the occupantand for his expected relative speed can be determined simultaneously inevaluation cycles which are independent of each other.

In accordance with an advantageous further embodiment of the presentinvention, the output signal a(t) of the sensor 10 is subjectedrepeatedly to a filtration, and therefore filtered at least twice. Theoutput signals a(t) and a_(w)(t) obtained by means of simple andrepeated filtration are then compared with each other and accumulated.The result of the comparison, in its turn, can be related to apresettable threshold value. If the result of the comparison lies abovethe presettable threshold value, then it can be concluded that there isan accident-produced change in the structure of the vehicle which forinstance has disadvantageous consequences for the length of the crushzone available. For example, a body part in the region of the crush zonemay break as a result of too high a load, so that no decrease in energyas a result of deforming work is possible any longer. Should such anevent occur, a comparison criterion for the reduction of the limitforward displacement value s_(g) and of the relative limit speed valuev_(g) can be obtained from the comparison between the function valueobtained by first filtration and the function value obtained by repeatedfiltration.

The acceleration time curve a(t) which is obtained, smoothed byfiltration, from the output signal a(t) of the sensor 10 is asubstantially sinusoidal function since, like the sine curve, it isunipolar in the first quadrant and rises continuously. In order to beable to effect an advance estimate of the future course of theacceleration and, on basis thereof, the future forward displacement ofthe occupant of the vehicle or his future relative speed with respect tothe passenger compartment, the function a(t) is advisedly approximatedby an easily calculated approximation function, for instance a sinecurve itself, or else a polynomial, preferably of the second or thirddegree. The function values determined in this way can in practiceadvantageously be stored in a storage element of the microcomputer 23 ofthe electronic device 20. In the case of an actual accident, theelectronic device 20 can then have access extremely rapidly to thestored table of values and, upon the advance estimate to be effected,determine whether function values of the function a(t) lying in thefuture or the values of forward displacement of the occupant and/or hisrelative speed which can be derived therefrom exceed the above-mentionedpresettable limit values or not. If the exceeding thereof is indicatedactivation of the safety means can be effected in due time so that adependable protection of the occupants of the vehicle is made possible.

The present invention will be explained below with reference to FIGS.10, 11 and 12, on the basis of a crash process which has actually takenplace. In this connection, the graph shown in FIG. 10 contains in itsupper part a limit curve formed of presettable limit values. In thiscase, the limit values are dependent on the time. The abscissacorresponds to the time axis, on which the time is plotted inmilliseconds. Increments of the corresponding limit value are plotted onthe ordinate. From the limit curve, it can be noted that, in the initialphase of the crash, which is assumed to start at the time t=0,comparatively large values of the limit value are preset. Thus, themaximum of the limit curve KG lies in the time interval between 10 andabout 15 milliseconds after the start of the crash and then drops offsubstantially continuously. This means that, with increasing duration ofthe crash process, the limit condition is made continuously moreprecise, since the limit values are continuously reduced. If the valuesdetermined by advance estimate exceed this limit curve, the safetydevice is activated, as will still be shown in the following.

FIG. 11 shows the output signal a(t) of the sensor 10 which the sensorgives off upon a crash. On the abscissa there is again plotted the timet in milliseconds, while positive and negative acceleration values inunits of the acceleration due to gravity g are plotted on the ordinate.Finally, FIG. 12 shows, combined in a single graph, the output signala(t) of the sensor 10 coming from a crash, together with the limit curveKG consisting of limit values and the function a(t) obtained byfiltration and possible approximation or possibly estimated in advance.An estimate in advance on the basis of the acceleration values measuredin the initial phase of the crash, with the aid of the smoothedacceleration curve obtained therefrom by filtration leads to the resultthat the curve a(t) would intersect the limit curve KG at a time ofabout 35 milliseconds after the start of the crash. The forwarddisplacement of the occupant of the vehicle would in this case be about15 cm. Based on this prediction, an activating of the protective meanswithin the time interval of 33.1 to 36.0 milliseconds after the start ofthe crash has been fixed.

What is claimed is:
 1. A method for protecting at least one occupant ofa vehicle which includes protective means for the at least one occupant,comprising the steps of:providing at least one acceleration sensorcoupled to the protective means for monitoring an acceleration of thevehicle, the at least one acceleration sensor having an output signalcorresponding to the acceleration; filtering the output signal with atleast one Kalman filter to obtain at least one of a first estimatedvalue of future forward displacement of the at least one occupant as afunction of the acceleration of the vehicle and a second estimated valueof future relative speed of the at least one occupant with respect to apassenger compartment of the vehicle; and activating the protectivemeans as a function of at least one of the first estimated value and thesecond estimated value when at least one of the first estimated valueexceeds first predetermined limit values within a predetermined futuretime interval and the second estimated value exceeds secondpredetermined limit values within the predetermined future timeinterval.
 2. The method according to claim 1, wherein the protectivemeans includes at least one of an airbag protection system and aseatbelt protection system and wherein the predetermined future timeinterval includes one of a known activation time of the airbagprotection system and a known activation time of the seatbelt protectionsystem.
 3. The method according to claim 1, wherein the protective meansincludes an airbag protection system and the predetermined future timeinterval is between 5 and 50 milliseconds after the start of a crash. 4.The method according to claim 3, wherein the predetermined future timeinterval is between 25 and 35 milliseconds after the start of a crash.5. The method according to claim 1, wherein the first predeterminedlimit values and the second predetermined limit values are determined asa function of at least one of a structure of the passenger compartmentof the vehicle and a structure of the protective means.
 6. The methodaccording to claim 5, wherein the first predetermined limit values arebetween 5 centimeters and 30 centimeters for the future forwarddisplacement of the at least one occupant of the vehicle.
 7. The methodaccording to claim 5, wherein the first predetermined limit values arebetween 10 centimeters and 20 centimeters for the future forwarddisplacement of the at least one occupant of the vehicle.
 8. The methodaccording to claim 5, wherein the second predetermined limit values arebetween 5 km/hr and 30 km/hr for the future relative speed of the atleast one occupant with respect to the passenger compartment of thevehicle.
 9. The method according to claim 5, wherein the secondpredetermined limit values are between 10 km/hr and 25 km/hr for thefuture relative speed of the at least one occupant with respect to thepassenger compartment of the vehicle.
 10. The method according to claim1, further comprising the steps of:filtering the output signal at leasttwice to provide a first filtered signal and a second filtered signal;comparing the first filtered signal and the second filtered signal toprovide at least one comparison value thereby indicating whether therehas been an accident-caused structural change of the vehicle;accumulating the at least one comparison value; and comparing the atleast one comparison value with at least one of the first predeterminedlimit values and the second predetermined limit values, wherein when theat least one comparison value exceeds at least one of the firstpredetermined limit values and the second predetermined limit values, acorrection criterion is derived for adjusting at least one of the firstpredetermined limit values and the second predetermined limit values.11. The method according to claim 1, wherein the first predeterminedlimit values and the second predetermined limit values are determined asa function of at least one operating parameter of the vehicle.
 12. Themethod according to claim 11, wherein the first predetermined limitvalues and the second predetermined limit values are determined as afunction of the duration time of an accident.
 13. The method accordingto claim 1, wherein the first predetermined limit values and the secondpredetermined limit values are made more precise after a predeterminedperiod of time as a function of an increasing duration time of anaccident.
 14. The method according to claim 1, wherein the output signalis approximated by an approximation function.
 15. The method accordingto claim 14, wherein the approximation function includes one of atrigonometric function and a low order polynomial.
 16. The methodaccording to claim 14, wherein approximation function provides at leastone approximation function value that is stored in a storage elementfrom which the at least one approximation function value can be readduring an accident.
 17. The method according to claim 1, wherein thefirst predetermined limit values and the second predetermined limitvalues form a limit curve formed by a convolution of a Gaussian functionwith a function obtained by at least one filtering of the output signalwith the at least one Kalman filter.
 18. A device for protecting atleast one occupant of a vehicle which includes at least one protectivemeans for the at least one occupant, comprising:at least oneacceleration sensor coupled to the protective means for monitoring anacceleration of the vehicle, the at least one acceleration sensor havingan output signal corresponding to the acceleration; and at least oneelectronic device for evaluating the output signal and controlling theprotective means in response to the output signal, the electronic deviceincluding,means for evaluating the position of the at least one occupantin the vehicle, means for determining at least one of firstpredetermined limit values for future forward displacement of the atleast one occupant as a function of the acceleration of the vehicle andsecond predetermined limit values for future relative speed of the atleast one occupant with respect to a passenger compartment of thevehicle, means for filtering the output signal with at least one Kalmanfilter to obtain at least one of a first estimated value of futureforward displacement of the at least one occupant as a function of theacceleration of the vehicle and a second estimated value of futurerelative speed of the at least one occupant with respect to a passengercompartment of the vehicle, and means for estimating whether at leastone of the first estimated value exceeds first predetermined limitvalues within a predetermined future time interval and the secondestimated value exceeds second predetermined limit values within thepredetermined future time interval and means for activating theprotective means as a function of at least one of the first and secondestimated values.